OUT OF RESONANCE INFRARED FLUORESCENCE OF SF6, (CF3I)-C-12, (CF3I)-C-13 IN QUASI-CONTINUUM STATES .1.

IR fluorescence of SF6 has been monitored in the spectral range 700-1300 cm-1 with a high sensitivity device, after IR multiphoton excitation at several vibrational energies up to 17 000 cm-1. Preliminary results have also been obtained for (CF3I)-C-12 and (CF3I)-C-13. The sensitivity achieved allows us to focus on the out of resonance fluorescence which turns out to be directly proportional to the local intramolecular couplings represented by the parameter gamma(E --> E') = pi-rho(E')\V(E --> E')\2. The method is partly free from an inhomogeneous contribution and the result can be compared to the Lorentzian model of intramolecular redistribution. It is shown that the gamma(E --> E') parameter exhibits a hierarchy of structures, the strongest couplings leading mainly to a perturbative redistribution, while the weakest couplings are responsible for the dissipative redistribution. The homogeneous dissipative part gamma(d) appears to be smaller than 1-1.5 cm-1.